Process for coating regenerated cellulose films



PROCESS FOR COATING REGENERATED CELLULOSE FILMS Max Morf, Beloeil, Quebec, Canada, assignor, by mes'ne assignments, to Du Pont Company of Canada Limited, Montreal, Quebec, Canada, a corporation of Canada No Drawing. Application November 25, 1953,

Serial No. 394,483

Claims priority, application Canada September 24, 1953 4 Claims. (Cl. 117-76) 7 2,726,171 Patented Dec. 6,

4" roll through unheated dip tanks containing, respectively, aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate as a 0.1% (by weight) solution in 10% aqueous glycerine, each sheet passing through only one of said tanks. The wet sheets were then passed over a guide onto two steam treated drying rolls at '95-100 C. and then through a dip tank heated to about 120 C. and containing a 7% (by Weight) xylene solution'of polyethylene, at a rate of about two feet per minute. From thepolythene tank, the sheets travelled directly into a tower where they were dried thronghcontact with a stream of hot air kept of regenerated cellulose with polyetylene instead of nitrocellulose compositions for the purposes of moisture-proofing the sheets or films as well as improving their resistance to mechanical damage and providing a heat seal stronger than that obtained with the said nitrocellulose compositions. In effect, this proposal was meant to produce sheets or films having all the desirable properties possessed by the known polyethylene sheets or films themselves but using considerably less polyethylene, the mechanical strength of the sheets or films being provided by a less expensive regenerated cellulose base sheet. It has, however, been heretofore impossible to obtain a satisfactory adhesion of the polyethylene to the regenerated cellulose base by any of the known coating processes and even the use of such eificient anchoring agents as stearato chromic chloride has proved unsuccessful, as reported by A. D. McLaren in The Journal of Polymer Science, vol. 3, pp. 652-62 (1948), and vol. 4, pp. 63-74 (1949).

The present invention purports to solve the aforementioned adhesion problem by providing new and very effective anchoring agents for polyethylene when applied as a coating to a regenerated cellulose base sheet or film.

It is therefore an object of this invention to provide an improved process for coating sheets or films of regenerated cellulose with polyethylene. Another object is to provide such an improved process using new anchoring agents for the polyethylene. Other objects will appear hereinafter.

These objects are accomplished, broadly, by first applying to the regenerated cellulose base sheet or film a member of the group consisting of aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, and thereafter coating said sheet or film with polyethylene.

In a more specific embodiment, the invention comprises first contacting the regenerated cellulose base sheet or film with a 0.02-0.2% aqueous solution of a member of the group consisting of aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, then drying the sheet or film at a temperature of 95100 C., and thereafter applying over the dried sheet or film a polyethylene coatmg.

In order more clearly to illustrate the invention, the following examples are given. It is, of course, to be understood that the invention is not limited to these precise examples which are merely illustrative of the invention. Obviously various other modifications will occur to those skilled in the art, which, however, do not depart from the nature or spirit of the instant invention.

Example 1 Six sheets of regenerated cellulose were passed from a at about 160 C., and thence over a water cooled head roll to a wind up roll. Each one of the sheets was then tested for adhesion of polyethylene to regenerated cellulose by the Scotch tape and heat seal tests, thus showing a good adhesion of the two materials to each other, particularly in the case of the iron, aluminum, copper and cobalt acetate-treated sheets.

The Scotch tape test was carried out by pressing a piece of Scotch tape firmly against the polyethylene coating and then pulling off.

The heat seal test was carried out as follows. Strips of polyethylene-coated film 1.5 x 4" were cut from the 4" sheet and then paired facing each other and sealed at C. with a standard bar sealer for nitrocellulose coated regenerated cellulose. The heat seal strength was then determined by fixing one end of the sample in a clip attached to a spring scale and pulling the other end by hand.

Example 2 The experiment of Example 1 was repeated but using 0.1% alcoholic solutions of the metallic acetates instead of aqueous solutions thereof and omitting the drying operation between the acetate tank and the polyethylene tank. Substantially similar results were obtained.

Example 3 The experiment of Example 1 was repeated using iron triacetate only as the anchoring agent, in the following concentrations as percentages by weight in 10% aqueous glycerine: 0.001, 0.010, 0.020, 0.040, 0.080, 0.100, 0.200 and 1.000. A good to excellent adhesion of the polyethylene to the cellulose was obtained with each concentration, the adhesion attaining its maximum with the 0.02-0.2% range of concentrations.

Since, as illustrated by the foregoing examples, the adhesion of polyethylene to regenerated cellulose is just as good with the use of the metallic acetates in aqueous solution as with the use of the acetates in solution in an organic solvent, it is preferable from the standpoints of economy and convenience to employ aqueous solutions of the acetates. This allows the metallic acetates to be incorporated directly in the aqueous softening bath for the regenerated cellulose, such as the glycerine bath, on the casting machine for producing regenerated cellulose sheets, and to be thus applied to the gel sheets as they pass through the glycerine bath. Example 1 illustrates the simultaneous treatment of the regenerated cellulose sheets with a softening agent and the anchoring agents of the present invention. The improved process of the invention thus requires no additional equipment over that used to produce regenerated cellulose sheets with a polyethylene coating and eliminates the inconvenience and expense of two coating operations.

As previously mentioned, the concentration of the anchoring agent solution may vary over a wide range. For best results, however, concentrations of from 0.02 to 0.2% by weight should be employed, preferably 0.1% by weight.

The foregoing examples also illustrate the application of the polyethylene coating to the treated regenerated cellulose sheet by passage of said sheet through a xylene solution of polyethylene having a specific concentration and heated to 120 C.

Polyethylene concentrations other than that given in the examples have been tested with equal success. However, using the aforementioned coating method, it was found that in order to obtain a clear polyethylene coating, the temperature of the coating bath should be at least 115 C. for polyethylene solutions containing a pure grade of high molecular weight polyethylene. Somewhat lower temperatures can be used for solutions containing low molecular weight polyethylene or an impure grade of polyethylene such as reclaim or previously extruded polyethylene.

It should be noted that other coating methods may be used with equal success for the application of the polyethylene to the regenerated cellulose base sheet as long as the latter is first treated with the new anchoring agents of this invention. The improved process of the invention is not limited to any specific method for applying the polyethylene itself.

Any variation or modification of the invention described above, which conforms to the spirit of the invention, is intended to be included within the scope of the claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I. In a process for coating a sheet or film of regenerated cellulose with polyethylene, the improvement which comprises first contacting said sheet or film with a solution containing from 0.02 to 0.2% by weight of a member of the group consisting of aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, and thereafter coating said sheet or film with polyethylene.

2. In a process for coating a sheet or film of regenerated cellulose with polyethylene, the improvement which comprises first contacting said sheet or film with an aqueous solution containing from 0.02 to 0.2% by weight of a member of the group consisting of aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, drying the wet sheet or film at a temperature of -l00 C., and thereafter coating the dried sheet or film with polyethylene.

3. In a process for coating a sheet or film of regenerated cellulose with polyethylene, the improvement which comprises first contacting said sheet or film with a solution containing about 0.1% by weight of a member of the group consisting of aluminum triacetate, iron triacctate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, and thereafter coating said sheet or film with polyethylene.

4. In a process for coating a sheet or film of regenerated cellulose with polyethylene, the improvement which comprises first contacting said sheet or film with an aqueous solution containing about 0.1% by weight of a member of the group consisting of aluminum triacetate, iron triacetate, copper diacetate, nickel triacetate, chromium triacetate and cobalt diacetate, drying the wet sheet or film at a temperature of 95 -100 C., and thereafter coating the dried sheet or film with polyethylene.

OTHER REFERENCES A. D. McLaren, The Journal of Polymer Science, vol. 3, pages 652-62 (1948). 

1. IN A PROCESS FOR COATING A SHEET OR FILM OF REGENERATED CELLUSLOSE WITH POLYETHYLENE, THE IMPROVEMENT WHICH COMPRISES FIRST CONTACTING SAID SHEET OR FILM WITH A SOLUTION CONTAINING FROM 0.02 TO 0.2% BY WEIGHT OF A MEMBER OF THE GROUP CONSISTING AL ALUMINUM TRIACETATE, IRON TRIACETATE, COPPER DIACETATE, NICKEL TRIACETATE CHROMIUM TRIACETATE AND COBALT DIACETATE, AND THEREAFTER COATING SAID SHEET OR FILM WITH POLYETHYLENE. 